Fusing apparatus with flashlamp circuit



T. a; MICHAELS 3,445,626 FUSING APPARATUS WITH FLASHLAMP CIRCUIT Filed May 2, 1966 LOGIC Q INTER- LOCK LOGIC TIMER LAMP f CONTROL FLASH I4 LAMP SENSOR ROLLER DRIVE LAMP CONTROL INVENTOR.

l THOMAS B. MICHAELS I ATTORNEYS United States Patent 3,445,626 FUSING APPARATUS WITH FLASHLAMP CIRCUIT Thomas B. Michaels, Rochester, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed May 2, 1966, Ser. No. 547,048 Int. Cl. H05b 1/02; F27d 19/00 US. Cl. 219-216 9 Claims ABSTRACT OF THE DISCLOSURE A control circuit for a flash fuser including logic circuit for sensing the passage of a recording medium to initiate a timing sequence to permit movement of the recording medium to a position under the influence of the fuser whereby the fuser is energized. Logic interlock circuit is provided to permit successive triggering of the fuser if a portion of the recording medium has not been subject to the influence of the fuser at some prior time.

This invention relates to a xerographic image fixing apparatus, and in particular, to an apparatus for permanently fixing electroscopic toner images onto print receiving record cards.

As known in the prior art, electroscopic toner may be a powder composition including one or more resins which are preferably thermoplastic in nature, a plasticizer which is a solvent that can act upon the resin at a temperature below the melting point of the resin, and a pigment for imparting a desired color to the toner material. Several electroscopic toner compositions are described in U.S. Patent No. 2,618,551, which issued to Walkup on Nov. 18, 1952.

When the unfused or unfixed toner is heated sufficiently, the toner will become molten and dissolve so that the solution will penetrate into the fibers of the media carrying the toner. Upon subsequent cooling, the toner image will become indelibly fixed in this media.

In the past, the heating of toner particles adhering to a latent electrostatic pattern on a dielectric recording medium, such as paper, in the fixing process of xerographic images has been accomplished in one manner through the use of a flash fuser. Such a fuser can be defined as an apparatus to selectively direct radiation from a fiashlamp onto the surface of the recording medium carrying the toner particles. This radiation is of such a nature as to sufficiently heat the toner to a molten state While leaving the recording sheet substantially unaffected.

In the case of uniformly sized recording sheets passing individually on a moving conveyor belt under the area of influence of a flash fuser, the fiashlamp can merely be pulsed on once for each sheet. However, with the advent of small computer read-out cards and data processing cards, it has become necessary to have a flash fuser which will effectively fuse toner on all areas of cards passing under the fuser regardless of the size of the cards. Therefore, it is easily appreciated that cards of various and random sizes present a problem to the prior art flash fusers which were designed to accommodate record cards of a uniform and predetermined size. This problem could not be solved without costly and cumbersome adjustments or conveyor speed and/ or area of fiashlamp influence. 1n addition to these undesirable solutions, it would also be possible to provide a flash fuser which flashes at an unusually high rate to insure that any card or portion thereof under the fuser at any one time would be subject to the toner-heating radiation of the fiashlamp. However, this solution would result in unnecessary operation of the lamp and therefore in an undesirable reduction in its longevity among other things.

In addition to the above considerations, the temperature stability of the control circuit for the flash fuser lamp must be great as required by the high ambient temperature environment to this circuit.

Therefore, it is an object of the present invention to provide an improved image fixing apparatus.

It is another object of the present invention to provide an improved flash fuser apparatus wherein toner particles on various and randomly sized recording media are effectively and efliciently fused as the recording media successively pass the apparatus.

Another object of the present invention is to provide an improved flash fuser apparatus wherein the longevity of the fiashlamp is maximized by utilizing a control circuit therefor which flashes the lamp only the requisite number of times to fuse all the toner on recording media.

It is another object of the invention to provide an improved flash fuser circuit which effectively and eifciently fuses the toner upon record cards passing within the influence of the fuser regardless of ambient environment-al temperature and card size.

These and other objects of the invention are accomplished in accordance with principles of the present invention by which sensing and logic circuits sense a first position of a record card relative to the fusing section. These circuits then initiate a timing circuit to permit movement of the detected card to a second position relative to the fusing section at which time the fiashlamp is triggered thereby fixing the toner pattern on the portion of the record card subject to the radiation from the fiashlamp. In addition, a logic interlock circuit permits the fiashlamp to remain untriggered in the absence of any record card to be fused. However, this interlock logic circuit also provides for successive triggering of the fiashlamp if a portion of the record card has not been subject to the radiation of the fiashlamp.

For a better understanding of the invention as well as other objects and features thereof, reference may be made to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIGURE 1 is a block diagram of the present invention;

FIGURE 2 is a detailed schematic of the present invention.

In FIGURE 1 there is illustrated a block diagram of the apparatus according to the present invention.

A record card generally designated 2 which carries an unfused toner particle pattern on its surface is transported by suitable roller-belt combinations generally designated 4 in such a manner as to intercept a beam of light passing through an aperture plate 6 behind which is located a conventional light source 8. This interception is accomplished immediately prior to the record cards entry into the area of influence of the fiashlamp assembly 10. Sensor 12 monitors, in effect, the future presence or absence of a record card under the fiashlamp assembly 10. Once a record card is detected by sensor 12 as entering the area of influence of the fiashlamp assembly 10, an appropriate sensor signal to this effect is translated to a logic circuit 14 as well as a logic interlock circuit 16. The logic circuit 14 determines from the sensor signal the presence or absence of a record card, or portion thereof, about to be available to the radiation from the fiashlamp assembly 10 and, accordingly, initiates a timing cycle in a timer circuit 18. This timer circuit is designed to permit a certain time period to expire before a signal is sent to the lamp control circuit 20 which trigger the fiashlamp in assembly 10 thereby fusing any toner particles to the record sheet then presently under the flashlamp assembly.

The signal from the timer circuit 18 which initiates the lamp control circuit 20 is also provided to the second of two inputs of the logic interlock circuit 16, the first input to the circuit being supplied from the output of the sensor 12 as referred to hereinbefore. The logic interlock circuit .16 performs the function of deciding the coincidence between a completed fusing cycle, i.e., the triggering of the flashlamp, and the absence of a record, or portion thereof, at the entry of the flashlamp area assembly 10. If this coincidence exists, the logic interlock circuit 16 provides a signal'indicative of this coincidence to the logic circuit 14 which holds the timer circuit 18 off. This olf condition of the timer circuit 18 is maintained until the sensor 12 and the logic circuit 14 detect another record card at the entry of the flashlamp area. The logic interlock circuit 16 will be described in more detail hereinafter in the description of the preferred embodiment of the present invention.

In FIGURE 2 there is illustrated a schematic of the flash fuser apparatus in accordance with a preferred embodiment of the present invention. A conventional transport system as shown includes rollers 22 and 24, the former being connected through suitable mechanical linkage generally designated by the broken line 26 to a conventional roller drive apparatus 28. A record card 2 is supported by one of the belts 30 which as shown carries an uufused toner particle pattern 32 on one of its surfaces. In the position shown in FIGURE 2, the leading edge or that edge nearest the flashlamp assembly intercepts the light ray which normally would be emitted by light source 8 through an aperture plate 6 to be focused by a suitable lens assembly 34 onto a photocell 35. The light source 8 receives its electrical power from a power supply of conventional design designated 36. The card 2 is conveyed by the roller-belt combinations at a predetermined and uniform rate into the area substantially under the reflector 38 of the flashlamp assembly 10. The assembly 10 includes a suitable fusing lamp 40, for example, a xenon gas lamp, which is electrically connected through a socket 42 to a conventional lamp control circuit 20, which could include a simple relay circuit or a controlled rectifier. When the fuser lamp 40 is flashed, or triggered on and off, the toner particles on the card 2, or portion thereof, under the reflector 38 are fused with the fibers of the record card 2.

As shown in FIGURE 2 the record card 2 is at a position immediately prior to entry into the area under the reflector 38 and hence the area of influence of the radiation from the flashlamp 40. The interruption of the light path between the light source 8 and the photocell 35 generates a signal which is amplified by a conventional amplifier 44 which has an output connected to the set side of a conventional flip-flop 46.

In its normal state, i.e., when there is no interruption of the aforementioned light path, the flip-flop 46 is in its reset condition. In this condition, the output from the reset side of the flip-flop is a signal at a voltage level of such polarity and magnitude when considered with the values of resistors 48 and 50 in the base circuit of an NPN transistor 52 as to bias this transistor in its conducting region. The emitter electrode 54 of the transistor 52 is directly connected to a reference potential, for example, ground potential, while its collector electrode 56 is directly coupled to one plate (hereinafter referred to as the ungrounded plate) of a capacitor 58, the other plate of which is directly grounded. Therefore, it may be seen that when the transistor 52 is biased in its conducting region, it affectively clamps the ungrounded plate of the capacitor 58 to ground thereby causing the same potential to be applied to both plates of this capacitor 58.

This condition with the same potential on both plates of the capacitor 58 prevents any charge accumulation by this capacitor from a constant current charging source which includes a PNP transistor 60 which has a collector electrode 62 directly connected to the ungrounded plate of this capacitor 58. The emitter electrode 64 of this transistor 60 is connected by way of a precision resistor 66 to a source of suitable positive potential applied at terminal 68. To provide a constant bias in the base circuit of this transistor 60, a voltage divider is connected to the base electrode 70 of this transistor 60 and includes an interconnected resistor 72 and a temperature-compensating Zener diode 74 which together are connected between the terminal 68 and ground potential.

When the aforementioned light path is interrupted, indicating entry of a record card to be fused into the area of the flashlamp assembly 10, the photocell 3-5 and the amplifier 44 provide an amplified signal indicative of this card position to trigger the flip-flop 46 to its set condition. In this set condition, the output from the reset side of this flip-flop is of such a polarity and magnitude as to render the transistor 52 nonconducting thereby removing the clamp ground potential from the ungrounded plate of capacitor 58. In this unclamped condition, the capacitor 58 is permitted to be charged to a potential dependent upon its capacitance value and the value of the emitter resistor 66 as well as the magnitude of the voltage applied at terminal 68. When this charge on the capacitor 58 accumulates to a value approximately equal to one half the voltage existing across the collector and base electrodes of the unijunction transistor 76, this transistor 76 will conduct. This conduction permits the capacitor 58 to discharge through its emitter-base junction and through the primary winding of the transformer 78. This discharge current through the primary winding of this transformer 78 is reflected in the secondary winding thereof by transformer action and supplied to the lamp control circuit 20 to ultimately trigger the flashlamp 40 thereby fusing any toner particles with the fiber of the record card, or portion thereof, under the reflector 38.

A signal indicative of the discharge of the capacitor 58 through the primary winding of the transformer 78 is translated to one of two inputs of an AND gate 80 which constitutes in part the logic interlock circuit 16 referred to in FIGURE 1. If the other input to this AND gate is enabled coincidentally with the arrival of the signal from the primary winding of the transformer 78 indicating a discharge of the capacitor 58, then this signal will be gated to the reset input of the flip-flop 46 thereby resetting this flip-flop. As aforementioned, upon the resetting of flip-flop 46 the ungrounded plate of the capacitor 58 is once again clamped to ground potential through transistor 52 thereby preventing a repetition of the charging and fusing cycle.

The other input of the AND gate 80 of the logic interlock circuit 16 is enabled during a condition in which the sensor 12 detects an absence of a record card at the entry to the flashlamp area, or, in other words, when the light path between the light source 8 and the photocell 35 is uninterrupted. As noted before, when this other input of the AND gate 80 is enabled coincidentally with the discharge of the capacitor 58, the flip-flop 46 is reset and the charging and fusing cycle is terminated until the flipflop is set again.

However, because of the unavoidable tolerances in the transport system itself as well as the charging circuit for the capacitor 58, a time constant circuit, such as resistor 82 and capacitor 84in the logic interlock circuit 16, is desirable to effect a less rapid change in unenabling signal level at the input to the AND gate 80 which is coupled to the sensor 12. In this manner, a card may be completely fused by a flash of the flashlamp 40 except for a small transverse section of the card extending from the trailing edge of the card to a short distance toward the leading edge thereof. This small transverse section of the car-d may occupy a position in the transport path of the card through the fuser assembly 10 located between the aforementioned path of light and the entry edge of the reflector 38. If this transverse section of the card has toner adhered thereto in an information pattern and there is too great of a spacing between the trailing edge of this card and the leading edge of the next card, or, this is the last card of a series of cards, the toner on this section will not be fused and this information lost. By the insertion of the time constant circuit 82-84, the enabling of the sensor input to the AND gate 80 is delayed momentarily after the absence of a card is detected by the sensor 12. This delay in the enabling of this input to the AND gate 80 insures that the charging cycle and hence the fusing cycle will be repeated once again regardless of the presence of a following card. It is understood that the values for the resistor 82 and the capacitor '84 may be chosen to provide any suitable delay which would be dependent upon the charging rate of the capacitor 58 as well as the transport speed of the roller-belt combinations moving the record card through assembly 10.

In view of the above remarks concerning the charging of the capacitor 58, it will be realized that the time required to charge the capacitor 58 to the requisite level to render the unijunction transistor 76 conductive should be correlated with the speed at which a record card is transported across the area under the reflector 38 of the flashlamp 40. For example, if the area of the reflector 38 has a dimension in the direction of card travel of four inches, and the transport speed is approximately two inches per second, then the requisite charge time for the capacitor 58 would be approximately two seconds.

While the invention has been described with reference to the circuit disclosed herein, it is not confined to the details set forth since it is apparent that certain electrical equivalent components may be substituted for the components of the preferred circuit without departing from the scope of the invention. Thus, for example, although a photocell and light source are utilized for detecting card position, it is apparent that a mechanical sensing device, such as a microswitch, may also be used for the same purpose.

Also, the signal at one input of the AND gate 80 indicative of the end of the charging and fusing cycle, or, in other words, the discharge of the capacitor 58, could be generated by a photoelectric monitor which could be located relative to lamp 40 to detect radiation therefrom.

While the motion of the record media past the fuser assembly has been described as uniform, it should be understood that this media could be stepped past the assembly as long as the stepping rate of this movement was correlated with the charging rate of the capacitor 58.

Therefore it is intended that the present invention cover such modifications or changes as may come within the scope of the invention as defined by the following claims.

What is claimed is:

1. A toner image fixing apparatus for fusing electroscopic toner particles with the fibers of record cards comprising:

(a) a selectively flash triggerable source of toner-heating radiation;

(b) means to direct said radiation over a pre-determined area;

(c) sensing means to generate a position signal indicative of a position of a record card relative to said predetermined area;

(d) logic means responsive to said position signal to generate an output signal;

(e) timer circuit means responsive to said output signal to repeatedly generate a timing signal over a predetermined time period; and,

(f) control means coupled to said source and responsive to said timing signal at the termination of said predetermined time period to flash said source of toner-heating radiation.

2. An apparatus according to claim 1 additionally including:

decision circuit means responsive to the coincidence of said timing signal and said position signal to prevent the generation of said output signal.

3. An apparatus according to claim 2 additionally including a timing circuit means to delay the response of said interlock means to said position signal.

4. A toner image fixing apparatus for fusing electroscopic toner particles with the fibers of record cards comprising:

(a) means to transport at a predetermined rate record cards through a first position and a second position, in that order, along a transport path;

(b) a selectively flash triggerable source of toner-heating radiation;

(0) means to direct said radiation over a predetermined area of said transport path, said second position being within said predetermined area and said first position being closely adjacent said predetermined area;

(d) logic means to generate an initiate signal when a portion of a record card is at said first position along said transport path; and,

(e) control means coupled to said radiation source and responsive to said initiate signal to repeatedly flash said radiation source when said portion of a record card is at said second position along said transport path.

5. An apparatus according to claim 4 additionally including:

AND gate means responsive to the coincidence of the flashing of said radiation source and the detected presence of a portion of a record card at said first position to effect continued application of said initiate signal to said control means.

6. An apparatus according to claim 5 additionally including:

a time constant circuit means coupled to said interlock means to delay for a predetermined interval the termination of said initiate signal upon the detected departure of a trailing edge of a record card from said first position.

7. A toner image fixing apparatus for fusing electroscopic toner particles with the fibers of record cards comprising:

(a) means to transport at a uniform speed record cards through first and second positions, in that order, along a transport path;

(b) a selectively flash triggerable source of toner-heating radiation;

(c) means for directing said radiation over a predetermined area of said transport path, said second position being within said predetermined area and said first position being closely adjacent said predetermined area;

(d) detector means to generate a position signal indicative of the presence of a portion of a record card at said first position;

(e) bistable circuit means coupled to said detector means and responsive to said position signal to change from one stable state to the other stable state;

(f) clamp means coupled to said bistable circuit means to effectively clamp a terminal to a predetermined potential when said bistable circuit means is in said one stable state and to unclamp said terminal when said bistable circuit means is in said other stable state;

(g) capacitive means connected between said terminal and said predetermined potential;

(h) circuit means for providing substantially constant current at said terminal;

(i) radiation source control means coupled to said radiation source to flash said source in response to a trigger signal;

(j) switch means coupled between said terminal and said control means to generate said trigger signal a predetermined time interval after said bistable circuit means changes to said other stable state and coincident with the presence of said portion of a record card at said second position;

(k) decision circuit means responsive to the coincidence of the detected departure of a trailing edge of a record card from said first position and the triggering of said radiation source to cause said bistable circuit means to return from said other stable state to said one stable state; and,

(1) time constant circuit means coupled between said detector means and said interlock means to elfectively delay the signalling of the detection of the departure of the trailing edge of the record card from said first position.

8. An apparatus according to claim 7 wherein:

(a) said bistable means includes a flip-flop having at least a set input, a reset input, and a reset output, and first circuit means to couple said set input to said detector means; and,

(b) said decision circuit means includes an AND gate having two inputs and an output, and second circuit means to couple one of said inputs to said time constant circuit means, and third circuit means to couple the other of said inputs to said switch means, and fourth circuit means to couple said output to said reset input.

9. An apparatus according to claim 8 wherein:

said claim means includes a transistor gate having a control and two output electrodes, said control electrode being coupled to said reset output, and one of said output electrodes coupled to said terminal and the other of said output electrodes being coupled to said predetermined potential.

References Cited UNITED STATES PATENTS 2,807,703 9/1957 ROshon 2l9--3'88 X 2,844,733 7/1958 Miller et a1 250-65 3,038,994- 6/ 1962 Nelson et a1. 250--65 3,163,755 12/1964 Kotz et al. 250-65 3,187,162 6/1965 Hojo et a1 219-388 RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner.

US. Cl. X.R. 

